Kingson Pocket Calculator (Simplex Slide Rule and Adder)

This pocket-sized sheet metal instrument combines a one-sided linear slide rule, an adder, and a rule. The sliding bar adder on the front has six bars. The upper parts are for addition, the lower parts are for subtraction, and round windows in the middle show the result. A metal stylus in a holder on the right side moves the bars, and a zeroing bar is at the top. The top is marked: Kingson (/) POCKET (/) CALCULATOR. A table of decimal equivalents is below the bars.

The back of the instrument is a slide rule with A and D scales on the base; B, CI (labeled as C1), and C scales on the slide; and a clear plastic frameless indicator. The slide may be removed to reveal a scale of 5.5 inches, divided to 32nds of an inch, and a scale of 14 centimeters, divided to millimeters. The right end of the slide is marked: KINGSON (/) MADE IN (/) BRITISH HONG KONG. The instrument fits in a blue plastic case marked: KINGSON (/) 4-RULE (/) CALCULATOR (/) ADD (/) SUBTRACT (/) MULTIPLY (/) DIVIDE (/) MADE IN HONG KONG (/) REGD. IN G. BRITAIN.

Metal adders were available from at least the 1920s. Compare 1986.0543.01, 1988.0807.04, 1989.0325.01, and 1989.0709.02. In 1937 Carl Kübler, whose German firm made the famous Addiator adder, filed a U.S. patent application for attaching an adder to a metal slide rule. By the 1950s an unknown company in Japan made "personal calculators" (such as 1992.0548.01 and 1981.0922.07) and sometimes attached slide rules. The design of this instrument is very similar to these, even though it was made in Hong Kong. Kingson also made a financial calculator for British currency before decimalization in 1971. For instructions, see 1994.0208.02.

According to a short 1973 article in the British journal Mathematics in School, the Kingson Pocket Calculator was sold at that time and had been "marketed for a few years." In Brussels in 1985, the donor purchased the instrument used. The previous owner may have operated an office supply store.

References: Carl Kübler, "Means for Mounting an Adding and Subtracting Device on Slide Rules" (U.S. Patent 2,153,089 issued April 4, 1939); "Kingson Pocket Calculator," The Centre for Computing History, http://www.computinghistory.org.uk/det/10923/Kingson-Pocket-Calculator/; D. J. Maxwell, "Apparatus Review," Mathematics in School 2, no. 2 (March 1973): 33.

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